Nine requirements for the origin of Earth's life: Not at the … · 2019-03-01 · Research Paper Nine requirements for the origin of Earth’s life: Not at the hydrothermal vent,

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Research Paper

Nine requirements for the origin of Earth’s life: Not at the hydrothermalvent, but in a nuclear geyser system

Shigenori Maruyama a,b,*, Ken Kurokawa a,c, Toshikazu Ebisuzaki d, Yusuke Sawaki e,f,Konomi Suda g, M. Santosh h,i, j

a Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8551, JapanbNovosibirsk State University, Pirogova 1, 630090, RussiacGenome Evolution Laboratory, National Institute of Genetics, 1111 Yata, Mishima, Shizuoka 411-8540, JapandRIKEN, 2-1 Hirosawa, Wako, Saitama, 351-0198, JapaneDepartment of Earth and Planetary Sciences, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo152-8550, JapanfDepartment of Earth Science and Astronomy Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, JapangGeomicrobiology Research Group, Institute for Geo-Resources and Environment, National Institute of Advanced Industrial Science and Technology (AIST), Central7, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, JapanhCentre for Tectonics, Resources and Exploration, Department of Earth Sciences, University of Adelaide, SA 5005, Australiai School of Earth Sciences and Resources, China University of Geosciences Beijing, 29 Xueyuan Road, Beijing 100083, ChinajKochi University, Kochi 780-8520, Japan

a r t i c l e i n f o

Article history:Received 18 January 2018Received in revised form12 June 2018Accepted 7 September 2018Available online xxxHandling Editor: E. Shaji

Keywords:Origin of Earth’s lifeNuclear geyser systemEmergence and evolution of lifeFalsifiability

* Corresponding author. Earth-Life Science Institute, T2-12-1 O-okayama, Meguro-ku, Tokyo 152-8551, JapaE-mail addresses: [email protected], maruyaPeer-review under responsibility of China University

https://doi.org/10.1016/j.gsf.2018.09.0111674-9871/� 2018, China University of Geosciences (BND license (http://creativecommons.org/licenses/by-n

Please cite this article in press as: Maruyamnuclear geyser system, Geoscience Frontiers

a b s t r a c t

The origin of life on Earth remains enigmatic with diverse models and debates. Here we discuss essentialrequirements for the first emergence of life on our planet and propose the following nine requirements:(1) an energy source (ionizing radiation and thermal energy); (2) a supply of nutrients (P, K, REE, etc.); (3)a supply of life-constituting major elements; (4) a high concentration of reduced gases such as CH4, HCNand NH3; (5) dry-wet cycles to create membranes and polymerize RNA; (6) a non-toxic aqueous envi-ronment; (7) Na-poor water; (8) highly diversified environments, and (9) cyclic conditions, such as day-to-night, hot-to-cold etc.

Based on these nine requirements, we evaluate previously proposed locations for the origin of Earth’slife, including: (1) Darwin’s “warm little pond”, leading to a “prebiotic soup” for life; (2) panspermia orNeo-panspermia (succession model of panspermia); (3) transportation from/through Mars, (4) a deep-sea hydrothermal system, (5) an on-land subduction-zone hot spring, and (6) a geyser systems drivenby a natural nuclear reactor. We conclude that location (6) is the most ideal candidate for the origin pointfor Earth’s life because of its efficiency in continuously supplying both the energy and the necessarymaterials for life, thereby maintaining the essential “cradle” for its initial development. We alsoemphasize that falsifiable working hypothesis provides an important tool to evaluate one of the biggestmysteries of the universe e the origin of life.

� 2018, China University of Geosciences (Beijing) and Peking University. Production and hosting byElsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/

licenses/by-nc-nd/4.0/).

1. Introduction

Some of the most important debates in modern science focus onthe origin of Universe, the origin and evolution of life, and the

okyo Institute of Technology,[email protected] (S. Maruyama).of Geosciences (Beijing).

eijing) and Peking University. Produc-nd/4.0/).

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development of human brain to acquire the knowledge that en-ables human beings to successfully inquire into the mysteries ofUniverse. The ancestors of modern life on Earth are thought to havehad appeared at about 4.1 Ga (Bell et al., 2015). This was during themysterious Hadean Eon, leaving no physical evidences except fortiny particles of zircon crystals (Wilde et al., 2001). However, it iscritical for the origin of life research to understand the Hadeansurface environment as the cradle of life and conditions thatgenerated and sustained life.

ction and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-

s for the origin of Earth’s life: Not at the hydrothermal vent, but in a16/j.gsf.2018.09.011

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S. Maruyama et al. / Geoscience Frontiers xxx (2018) 1e212

Hypotheses of birthplace of life have been proposed since Dar-win’s time. These include the following: (1) the classic concept of‘Darwin’s warm little pond’, involving an organic soup either on-land or in tidal flats (Darwin, 1859; Oparin, 1957; Deamer, 1997),(2) the panspermia model that explains life as arriving from theextraterrestrial Universe (Arrhenius, 1908) and Neo-panspermia assuccession model of Panspermia (Sutherland, 2016), (3) the ideathat life was originated fromMars (Kirschvink andWeiss, 2003), (4)the proposal that life was initiated in a mid-oceanic ridge hydro-thermal system (Corliss et al., 1981) or in an alkaline hydrothermalvent (Kelley et al., 2001), (5) the idea that life was born under islandarc volcanic environments related to a primordial continent(Mulkidjanian et al., 2012), and (6) the recently proposed nucleargeyser model that life was born at geyser environment driven by anatural nuclear reactor on the Hadean primordial continent(Ebisuzaki and Maruyama, 2017) (Fig. 1). However, conditions tobear life have not yet clearly defined in previous studies. In thispaper, we pick up significant requirements for the birthplace of lifewith reasonable justification. Based on these requirements, weevaluate respective birthplace hypotheses and speculate the mostlikely site is for life’s birthplace.

2. Models for the birthplace of life

Fig. 1 summarizes hypotheses for the birthplace of life on Earth.In following section, each hypothesis is briefly introduced.

2.1. The classic concept: small ponds on land or a shallow marineenvironment (tidal flats)

Since Darwin’s time, it has been generally considered that tidalflats along the continental margins could provide an ideal

Figure 1. Proposed sites for the birthplace of life on Earth. (1) Classic concepts, including Darflat (Oparin, 1957), (2) Panspermia (Arrhenius, 1908) or Neo-Panspermia (Sutherland, 2016)(Corliss et al., 1981) or in an alkaline hydrothermal vent (Kelly et al., 2001), (5) a hydrothermgeyser system on the Hadean primordial continent (Ebisuzaki and Maruyama, 2017).

Please cite this article in press as: Maruyama, S., et al., Nine requirementnuclear geyser system, Geoscience Frontiers (2018), https://doi.org/10.10

environment for the emergence of life. The classic concept of‘Darwin’s warm little pond’ (Darwin, 1859) was the first insightfulmodel to explain life’s emergence. The “warm little pond” wasconsidered to provide essential requirements for the formation oflife, including supplies of ammonia and phosphoric acids, as well aslight, heat, electricity, and other factors that facilitated the syn-thesis of complex organic compounds through the repeated dry-wet cycles and dehydration-hydration cycles, though these fac-tors were not initially considered very deeply. Subsequently, Oparin(1924, 1957) suggested that life was generated in “coacervates”,which are immiscible semi-permeable spherical droplets of mi-celles comprising large organic molecules that rained into the seafrom a reduced atmosphere. However, the reduced Hadean atmo-sphere that Oparin (1924, 1957) and Miller (1953) assumed hasbeen refuted by later numerical calculations for Earth’s primordialatmosphere, suggesting that there were oxidized CO2eH2OeN2compounds comprising an atmosphere that achieved a surfacepressure of about 400 bars shortly after Earth’s formation (e.g., Abeand Matsui, 1986; Zahnle et al., 1988). These results question thevalidity of the classic concept.

2.2. Panspermia and Neo-Panspermia

The model of panspermia was proposed by Arrhenius (1908),who suggested that the first life was extraterrestrial, and that itcame to Earth from sources that are spread through the universe.This model is based on an assumption that life was initiated andevolved elsewhere in the universe, perhaps even very early in theevolution, subsequently spreading throughout space. In spite of thelack of direct evidence, some researchers continue to support thisconcept (e.g. Crick and Orgel, 1973; Hoyle and Wickramasinghe,1999). According to this model, life forms that ultimately arrive at

win’s warm little pond (Darwin, 1859) with a primordial soup, or a shallow marine tidal, (3) Mars (Kirschvink and Weiss, 2003), (4) a mid-oceanic ridge hydrothermal systemal environment with island arc volcanoes (Mulkidjanian et al., 2012), and (6) a nuclear


S. Maruyama et al. / Geoscience Frontiers xxx (2018) 1e21 3

Earth are able to survive long-term travel during temperatures of�270 �C that prevail in space. Also life would be able to survive thevery high temperatures achieved when its carriers (comets, me-teors) penetrated Earth’s atmosphere and collided with the surface.

Recently a hybrid variant of the panspermia theory has beenproposed, which we tentatively name the “Neo-Panspermia”model. This theory hypothesizes that meteors and/or cosmic dustdeliver to Earth the advanced building block of life (BBL) such asglycol aldehyde, cyanamide, urea, cyanoacetaldehyde, cyanoace-tylene, and schreibersite as well (e.g., Sutherland, 2016). Discov-eries of organic matter fromMurchisonmeteorite (Levy et al., 1973)and Tagish Lake meteorite (Pizzarello et al., 2001; Sephton, 2002)indicate the possibility of organic material delivered from the outerspace. This model claims that Earth’s life can be automaticallygenerated if the necessary BBLs are constantly supplied from thespace to an appropriate point on Earth’s surface, such as a pond onthe landmass (Fig. 2).

2.3. Mars origin

Recent ideas suggest that the first life originated on Mars andwas subsequently conveyed to Earth within a meteorite (McKayet al., 1996; Sleep and Zahnle, 1998; Weiss et al., 2000; Kirschvinkand Weiss, 2003). According to this model, early Mars provided abetter habitat for the initiation of life than did Earth, and a Martianlifeform could be transferred to Earth by ejection during an impactevent. Because Mars’ gravitational acceleration is much lower thanthat of Earth (Mars’s size is one tenth of that of the Earth), thisejection mechanism is much more likely to have occurred as aMars-to-Earth transfer than the reverse. Evidence of “microor-ganisms” in one particular Martianmeteorite. The Allan Hills 84001(ALH84001) was offered in support of this model (McKay et al.,1996; Thomas-Keprta et al., 1998, 2000, 2001).

2.4. Deep-sea hydrothermal vents at mid-oceanic ridge

Previous studies reported the discovery of hyperthermophilemicrobes in the mid-oceanic ridge (MOR) hydrothermal vents in adeep-sea environment with an average depth of 2.5 km (e.g. Corliss

Figure 2. The model of Neo-Panspermia. The Neo-Panspermia model proposes that meteorEarth’s ocean and atmosphere, and constantly do so even today.


et al., 1981; Barros and Hoffman, 1985), where various microor-ganisms are observed and survive up to temperatures of 130 �C (e.g.Jannasch and Mottl, 1985). Moreover, several large multi-cellularanimals, such as mussels (Smith, 1985) and shrimps (Nuckleyet al., 1996), are also found where sunlight does not reach (e.g.,Baross and Hoffman, 1985; Gold, 1992; Deming and Baross, 1993;Wirsen et al., 1993). The presence of this ecosystem in the deepsea, using chemical energy rather than sunlight, is regarded as oneof the breakthrough findings of the diversity of biological envi-ronments. Life is known to be tough and robust even in extremeenvironments, such as extremely low-temperature region(< �50 �C in winter) on Antarctica or Himalaya-Tibet regions.Therefore, it has been considered that life could survive even indeep sea with high temperature and no sunlight. In particular, thediscovery of hyperthermophile microorganisms in this environ-ment led many biologists to presume that the birthplace of life is atmid oceanic ridge, because, according to the phylogenic tree of lifebased on ribosomal RNA, thermophile microorganisms plot veryclose to the root of life between the two domains of bacteria andarchaea (Woese et al., 1990) (Fig. 3).

Besides this discovery, geochemical evidence looked supportingthe MOR as the birthplace of life, because recent studies haverevealed that hydrogen is released at MORs through the process ofserpentinization where peridotite is exposed (Charlou et al., 2002;Takai et al., 2004; Kelley et al., 2005; Russell et al., 2010). It has longbeen considered that hydrogen as a reduced gas can promote thesynthesis of amino acids, as clearly demonstrated by the early ex-periments of Miller (1953), who produced amino acids through gasflow experiments with ammonia, hydrogen, carbon monoxide,methane, and water vapor as starting materials. Therefore, theproduction of hydrogen at MOR was assumed to play an importantrole for the birthplace of life.

Geologists have also known that mid-oceanic ridge basalts(MORBs) in the Hadean Earth were not similar to those of modernEarth. Because of the higher mantle potential temperatures by over300 K, the Hadean MORB magmas were mostly komatiites (e.g.Takahashi, 1986), which are compositionally similar to peridotitesor serpentinites. Thus, the Hadean MORBs must have producedevenmore hydrogen, and providedmore reduced conditions due to

s and/or cosmic dusts deliver necessary BBLs for generating life, after the formation of


Figure 3. Phylogenetic tree of life by Woese et al. (1990). The relationships among Eukarya, Archaea and Bacteria are shown, all having evolved from Progenote (Woese and Fox,1977) or LUCA, the “last universal common ancestor” (Fox et al., 1980). Note that all living organisms are plotted at the tops of tree branches, and are connected their rootsdownwards to the LUCA. If parallel gene transfer is common, the tree of life does not indicate genetic relationships, particularly before 2.0 Ga (Doolittle, 1999). However, if evolutionis dominantly controlled by increasing pO2 after 2.0 Ga, then the tree of life could be reconstructed as a function of pO2. In that case hydrogenobacteria and sulfur bacteria could bethe most primitive microbes in terms of their functional genes.


serpentinization. These factors lend support to the theory that thelife originated during Hadean or Archean MOR (Russell et al., 1988,1994; Russell and Hall, 1997; Kelley et al., 2001, 2005; Martin andRussell, 2003). Thus, the creation of the organic world from inor-ganic material marks a turning point in Earth history, and deep-seahydrothermal systems at MOR has been thought to be the birth-place of first life, termed “LUCA(s)” for “last universal commonancestor(s)” (Fox et al., 1980).

Table 1Approximate concentrations of key ions in various environments. Mulkidjanian et al.(2012) focused on ubiquitous ions and primitive proteins with some functional andfundamental systems, and showed the necessity of Kþ, Zn2þ, Mn2þ and PO4

3� tomaintain vital functions. According to their model, proto-cells must have evolved inhabitats with a high K/Na ratio, with relatively high concentration of Zn andMn, andphosphorous compounds, like phosphate.

Ion Modern sea water(mol/L)

Anoxic water ofprimordial ocean(mol/L)

Cell cytoplasm (mol/L)

Naþ 0.4 >0.4 0.01

2.5. Island arc volcanoes; hydrothermal field

Mulkidjanian et al. (2012), summarizing geochemical re-quirements with phylogenomic scrutiny of the inorganic ions asthe universal components of modern cells, reconstructed thehatcheries of the first cells as the birthplace of life. They focusedon ubiquitous ions and primitive proteins with some functionaland fundamental systems, and showed the necessity of Kþ, Zn2þ,Mn2þ and PO4

3� to maintain vital functions. According to theirmodel, proto-cells must have evolved in habitats with a high K/Na ratio, with relatively high concentration of Zn and Mn, andphosphorus compounds, like phosphate (Table 1). Because P doesnot react chemically in an oxidized environment, an anoxic at-mosphere must have existed at the time of life’s origin. Theyproposed that the most probable site for meeting these re-quirements was fumaroles on primordial continent, where vol-canic gas was erupted (Fig. 4). Volcanic gas from fumaroles doesnot include much Na, and K is dominant. Also the concentrationof K is relatively high in the volcanic front of subduction zones,more so than in the case of MORBs, and fumaroles can concen-trate more K in the vapor phase from the primary magma.

Kþ 0.01 w0.01 0.1Caþ 0.01 w0.01 0.001Mgþ 0.05 w0.01 0.01Fe 10�8 (mostly Fe3þ) 10�5 10�3e10�4

Mn2þ 10�8 10�6e10�8 10�6

Zn2þ 10�9 <10�12 10�3e10�4

Cu 10�9(Cu2þ) <10�20(Cuþ) 10�5

Cl� 0.5 >0.1 0.1PO4

3� 10�6e10�9 <10�5 w10�2 (mostly bound)

2.6. Geyser system driven by a natural nuclear reactor

The nuclear geyser model is recently proposed hypothesis forthe birthplace of life by Ebisuzaki and Maruyama (2017). Thebreakthrough of this hypothesis comparing to previous models isthat they clearly stated the necessity of (1) extremely high energydensity to promote prebiotic chemical evolution, and (2) the


energy/material circulation to mix up reducing and oxidizing ma-terial to produce BBL.

First, they pointed out extremely high energy density isrequired to produce fundamental BBLs including reducing gasesto lead for the emergence of life, and only one solution is ionizingradiation by natural nuclear reactor composed of uranium ore.Living organism is made up of carbon (C), hydrogen (H), oxygen(O), and nitrogen (N). More than 95% of the bulk composition ofliving organisms consists of these four elements. CO2, H2O, andN2 are the major sources for C, H, O, and N to produce BBLs. Yet,CO2, H2O, and N2 are thermodynamically very stable on thesurface environments on both the modern and Hadean Earth.Therefore, despite being the most critical element for synthe-sizing amino acids, it is significantly difficult to synthesize NH3from N2 in the atmosphere to utilize for synthesizing BBL. Toovercome this difficulty, a natural nuclear reactor is the mostideal. This is because the ionizing radiation from a natural nu-clear reactor can break down triply bonded N2 into protons,


Figure 4. The birthplace of life at an island arc fumarole (Mulkidjanian et al., 2012). K-rich water on land can be made through two steps of fluid separation; first directly from themagma (left), which is then followed by K-rich fluids emanating from fumaroles by liquid or vapor separation (middle and right).


neutrons, and large number of electrons in areas adjacent to auranium ore body, and the same thing will happen for othermaterials, such as CO2, H2O, and organic matter. All these ma-terials are broken into high energy radical particles such asaqueous electrons. After such a process, broken substances reactwith each other to form other material including BBLs.

In addition, they explained systematic energy/material circula-tion as a key to synthesize more complex organic compounds. Theycombined natural nuclear reactor (uranium ore) and geyser to

Figure 5. The nuclear Geyser model as the birthplace of first life. (Left) Schematic figure of tmain cave is filled with water and it boils up, geyser splash will toss off something from thperiodic splash of the geyser by continuously supplying surface water. The natural nuclear rphases. The exposed wall rocks of the geyser are not only uranium ore but also KREEP basalshaped ceiling of cave works as the container of reduced gasses to enable the synthesis of amthe reactor room, it remains dormant. Once water covers the reactor, it becomes an active phare two types of potential heat source; either the volcanic magma or the natural nuclear reBBLs.


propose a new hypothesis named Nuclear Geyser model (Fig. 5).According to this model, a natural nuclear reactor provides abun-dant high energy particle through ionizing radiation to promotechemical reaction to produce numerous BBLs. Basically, reducingmaterial is produced underground while oxidizing material appearon the surface environment. Geyser splash drives mixing ofreducing and oxidizing material. Through the activity of nucleargeyser system, primordial life is assumed to be born. Also theyexplained this site could supply all necessary components to

he nuclear geyser system. Surface river water drains into underground caves. Once thee cave onto surface environment. A necked narrow passage connecting caves controlseactor works periodically depending on its water content, between dormant and activet, serpentinite, and schreibersite (Fe3P) that supply important nutrients. The irregular-ino acids. (Right) The fundamental mechanism of the geyser. While water does not fillase. When the underground cave is filled with boiled water, it splashes. Although thereactor, the latter is emphasized in this model to promote chemical reaction to produce



generate life, such as HCN, nitriles, glyceraldehyde, and glyco-laldehyde (Fig. 6).

The original proposal for a natural nuclear reactor was byZel’dovich and Khariton (1940a, b), and Kuroda (1956) theoreticallypredicted that a natural nuclear reactor would be found on theEarth. Such a natural nuclear reactor was then discovered in theGabonese Republic in central Africa in 1972 (Bodu et al., 1971;Neuilly et al., 1972; Gauthier-Lafaye and Weber, 2003; Ndongoet al., 2016). Through discussions about natural nuclear reactorsand related radiation effects to promote the chemical reactions toform organic compounds, some recent proposals were made thatsuch reactors could have contributed to beginnings and evolutionof life (e.g. Adam, 2016). However, Ebisuzaki and Maruyama (2017)first proposed a comprehensivemodel of a nuclear geyser system asthe birthplace of Earth life with the mechanism to form necessaryBBL.

3. The birthplace of life: key factors

Since Darwin’s time, necessary conditions or environmentalsetting for the emergence of life has long been discussed, althoughprevious studies generally focused on a few aspects of life’s emer-gence, and did not evaluate the essential points. For example, thetopic of the formation of cell membrane, or synthesis of some sort

Figure 6. Chemical reaction proceeding in a natural nuclear geyser. (Left) Diagram shows chnatural reactor, each material does not react with each other, remaining as H2O, N2, HCHO, HC1 and 2. This occurs because of the lack of activation energy. (Right) Reaction process in thehigh-energy particles, such as aqueous electrons, are provided to promote chemical reactilaldehyde to form other complex organic compounds. Ionizing radiation provides the only


of organic compounds, have been investigated, but it has not beenproposed howandwhere both reactions proceeded to form life. Wesummarize the necessary conditions for birthplace of life based onthe review of previous multidisciplinary studies ranging frombiological to astronomical viewpoints. Based on these, we identifynine requirements for the emergence of life on a planet (Table 2). Inthe following section, we evaluate the significance of each ofrequirements.

3.1. Energy source: ionizing radiation (non-thermal energy) andthermal energy

To synthesize organic compounds, it is well known that nitrogen(N) is required for chemical reactions to proceed in spite of verystrong triple bonding of N2. To break this triple bonding, the Haber-Bosch process was invented, utilizing high temperatures(500e600 �C) and high pressures (200e1000 atm) to facilitate re-actions of N by overcoming a high activation energy barrier. Innature, however, such conditions cannot be maintained to facilitatethe necessary reactions of N to produce BBL.

To initiate chemical reaction of triply bonded N2, a reasonableenergy source is radioactive non-thermal energy during uraniumdisintegration and it is the only one solution to destabilize N2 aswell as H2O, and CO2 to facilitate chemical reaction. The necessary

emical material in the dormant phase. During dormant phase or low radiation levels ofN, amino acids, and fatty acids. There are two large activation barriers shown as Barrier

active phase. Once the system reaches the level to activate the geyser system, abundanton between any kind of available material, such as nitriles, glyceraldehyde and glyco-means to overcome activation energy problems (Ebisuzaki and Maruyama, 2017).


Table 2Nine requirements for emergence of life. For the emergence of life on the planet,there are several essential requirements to be fulfilled. See text for discussion.

Environmental factors Nucleargeysersystem

Hydrothermalsystem

Marsc Universed

1 Energy source (ionizingradiation þ thermal energy)

Yes No Yes Yes

2 Supply of nutrients (P,K, KREEPetc.)

Yes ? a Yes No

3 Supply of life constituentelements (C, H, O, N)

Yes ? a Yes Yes

4 Concentration of reducing gas Yes No ? b No5 Dry/wet cycle Yes No Yes No6 Na-poor water Yes No Yes No7 Non-toxic water environment Yes No ? b No8 Diversified environments

(Ocean: pH, salinity, heavymetals, Atmosphere:Temperature & Pressure,Continent: varied geology)

Yes No ? b No

9 Cyclic change Yes No No No

a For some elements, Yes. But for others, No.b No evidence, but presumably Yes.c Mars kept ocean for the first 400 million years after the formation.d Universe does not have liquid water in the matrix.


reactions would be particularly effective in close proximity to thecore of the natural nuclear reactor, where nearly all moleculeswould be broken. With increasing distance from the core of thenatural nuclear reactor, the broken molecules (high energy in-termediates) would start reacting to synthesize both inorganic andorganic matter with the supply of abundant electrons from thenuclear reactor. These are the distinct advantages of a natural nu-clear reactor for promoting the chemical reactions needed to syn-thesize organic compounds, including a wide variety of BBLs(Ebisuzaki and Maruyama, 2017). Through a continuous supply ofaqueous electrons and active chemical products, numerous kinds ofsimple or macromolecular organic compounds will be produced. Anatural nuclear reactor is only one supplier of high energy enoughto facilitate production of BBL on Hadean Earth (Fig. 6).

The important point here is that thermal energy cannot play arole as same as non-thermal energy because organic compoundsare broken at temperatures above 100 �C. Because the ionizingradiation from a natural nuclear reactor is a non-thermal energysource, it is a key to promote the synthesis of organic compounds.On the Hadean Earth, such natural nuclear reactors were likely verywidespread because the primordial continental crust was remark-ably enriched in uranium (U) and thorium (Th) (Ebisuzaki andMaruyama, 2017). The remnant of such a natural nuclear reactorformed at 2.3e2.2 Ga has beenwell-documented at the Oklo site inGabon Republic, Central Africa (Bodu et al., 1971; Lancelot et al.,1975). This example suggests that similar natural nuclear reactorscould be present on the Hadean continental landmass, particularlydue to the high concentration of U in Hadean landmass. Because Ucannot enter the crystal structure of mantle minerals, such asolivine or pyroxene due to its large ionic radius, U concentrations inthe Hadean crust could have been 1000 times more than that in thepresent day mantle. This high abundance of U functioned as anatural nuclear reactor, and it could have served as the energysource to promote the chemical reactions for forming BBLs(Maruyama and Ebisuzaki, 2017).

3.2. Supply of nutrients (K, REE, P, etc.)

C, H, O, and N make up 95% of living organisms, and theremaining 5% is made up by nutrients such as potassium (K),phosphorus (P), iron (Fe), calcium (Ca) and magnesium (Mg). C, H,


O, and N are supplied by the atmosphere and ocean, while theremaining nutrients are derived from the landmass, which providesa total of 29 elements including minor and trace elements (Ochiai,2008). Although nutrients are minor constituents, living organismscannot emerge without them.

On the modern Earth, the essential nutrients for life are derivedfrom granitic continents enriched in K, P, rare earth elements(REEs), and other elements. However, on the Hadean Earth,immediately after the consolidation of its magma ocean, granitewas not present, because the formation of granite only occurredwhen plate tectonics began. Although the operation of plate tec-tonics initiated after the appearance of the ocean between 4.37 Gaand 4.20 Ga (Maruyama et al., 2018), a sufficient amount of graniticrocks could not have accumulated during Hadean time. Thus, thefirst life required an alternative source of nutrients thanwhat couldbe supplied by granites.

The alternative source must be the primordial continents, whichwould be rocks similar to those currently exposed on the Moon.These rocks are dominantly anorthosite together with KREEP ba-salts (Arai and Maruyama, 2017; Dohm et al., 2018). KREEP basaltwas formed after 85% of the Moon’s magma ocean solidified,resulting in a final residue of Fe-rich basaltic melts (Arai andMaruyama, 2017). The petrochemical characteristics of KREEPbasalt include enrichment or super-enrichment in (1) high fieldstrength elements (HFSE), such as zirconium, niobium, hafnium,REE, thorium, uranium and tantalum, and (2) large ion lithophileelements (LILE), such as potassium, rubidium, caesium, strontium,and barium. The final 15% residue must have (1) solidified to be themafic lower crust under the primordial continents, (2) intrudedinto the upper felsic crust, or (3) erupted on the surface of theprimordial continents. The nutrients derived from primordialcontinent must have played a critical role in feeding the first life onthe primordial continents.

3.3. Supply of life’s main constituent elements (C, H, O, and N)

No one has questions about the necessity of C, H, O, and N forlife, because more than 95% of individual body of living organism iscomposed of C, H, O, and N. Combined with the supply of nutrients(K, REE, P, etc.) (as stated at section 3.2), the supply of life-constituting elements (C, H, O, and N) is critical to sustain life. Aconcept of the “Habitable Trinity” (Dohm and Maruyama, 2015)simply shows such a condition, which holds that the co-existenceof suppliers of all necessary elements; i.e. the atmosphere, ocean,and landmass, and the supplying system is driven by the Sun,promoting material and energy circulation (Fig. 7). Most planetaryscientists adhere to a prevailing concept of the habitable zone,focusing on the presence of liquid water. They regard this conceptas the most important condition for the potential presence of life,however, living organisms cannot survive with water only. Thepresence of the Habitable Trinity conditions must be emphasized inconsidering the emergence and survival of life.

3.4. Concentration of highly reduced gas

Prebiotic chemistry requires reducing material, such as H2, CO,CH4, NH3 and HCN, to promote the synthesis of amino-acids to leadto the origin of life (Miller, 1953; Bada and Lazcano, 2003;Sutherland, 2016). This was clearly demonstrated in the early ex-periments of Miller (1953). However, major difficulties arise in themechanism to accumulate these gasses in nature. Reduced gassesare diffused into open atmosphere or ocean, after they are pro-duced through serpentinization, which is the case at mid-oceanicridges or surface environment. To overcome this problem, an


Figure 7. Habitable Trinity model. To evolve into a habitable planet, co-existence ofatmosphere, ocean, and landmass with a driving force (Sun) is one of the most criticalcondition. It is obvious that life cannot live with water only. The supply of nutrientsderived from landmass is critical for the emergence of life (Dohm and Maruyama,2015).


underground cave is an ideal site, because the reducing gas pro-duced could be accumulated over time on the ceiling of the cave.

3.5. Dry-wet cycles

Alternating dry and wet conditions are necessary for theemergence of life, as exemplified by a suite of diverse prebioticchemical reactions including polymerization of amino acids topeptides and synthesis of RNA from nucleotides by repeateddehydration-hydration in tidal flats, that has been repeatedlyemphasized (e.g. Oparin, 1957; Miller, and Urey, 1959; Miller andBada, 1988; Deamer, 1997, 2016; Damer and Deamer, 2015). Thetidal impact of the Moon was much stronger during the Hadeanthan at present. While the modern Moon’s effects cause repeateddry and wet conditions on tidal flats twice a day, this cycle musthave been every 5 hours in the early Hadean, immediately afterthe Giant Impact (Benz et al., 1989; Canup and Asphaug, 2001). Itis worthwhile to recall that the presence of a landmass on theHadean Earth inevitably leads to conditions that make the for-mation of BBLs possible by dry-wet cycles. If no landmass wouldbe present, the resulting ocean planet could not have the dry-wetcycles. Such a planet could not lead to the stepwise synthesis ofBBLs.

3.6. Non-toxic water environment (less salt, less heavy metals, andneutral pH)

For life, water must be moderately clean, which we call non-toxic water environment. The reason why we emphasize it as oneof requirements is Hadean ocean was too toxic to live.

Based on the recently proposed ABEL model (Fig. 8; Maruyamaand Ebisuzaki, 2017), the solid Earth was formed by enstatitechondrite-like dry material at 4.567e4.530 Ga, and water compo-nents were secondary accreted through ABEL Bombardment be-tween 4.37 Ga and 4.20 Ga by carbonaceous chondrites from outerasteroid belt. Enstatite chondrites contain sulfur and halogens, suchas Cl, in addition to schreibersite (Fe3P), which must have beenconcentrated on the primordial continents through solidification ofmagma ocean because they cannot enter into mantle silicates


(Pasek, 2015; Maruyama and Ebisuzaki, 2017). Moreover, carbo-naceous chondrites are composed of not only large amounts of H2O,but also CO2, N2, SO2, halogens such as Cl and F (McDonough andSun, 1995). Through the ABEL Bombardment, halogens andmetallic elements were dissolved into accreted H2O, which formedthe primordial ocean, indicating that the primordial ocean musthave been remarkably toxic with ultra-high acidity and salinity, aswell as a high abundance of heavy metallic elements. According toestimates of the chemical composition of the primordial ocean byaveraged volatile composition inferred from CI chondrite compo-sitions (e.g., Maruyama et al., 2013), it must have been about 50%sulfidic and 50% H2O with considerable amounts of HCl, HNO3, andHF, suggesting a pH < 0.1. Under such highly acidic condition, largeamounts of metallic elements such as Fe, Mn,Mg, Cu, Zn, Pb, Mo, Hgwould be dissolved in the ocean. Moreover, salinity in the Hadeanocean must have been 5e10 times more than today (Saito et al.,submitted). Hadean MORs would be covered by such a highly toxicocean. These constraints do not permit Progenote(s), or LUCA(s) toappear in an ocean.

To overcome this difficulty for the emergence of life, a hugelandmass is necessary, because clean water gets accumulated on alandmass as forms of ponds, lakes, swamps, or wetlands throughglobal hydrological circulation by the climate system, where proto-life could utilize water to evolve into the first life.

With time, water-rock (landmass) interactions can change thechemistry of the primordial ocean through hydrological materialcirculation. Water-rock interaction is due to reaction betweenflattered rock particles and water. To flatten rocks, weathering,erosion, and transportation process is necessary, which is enabledby the presence of landmass, but it will take a very long time. Forexample, even at the onset of Phanerozoic, ca. 600 Ma, the salinityof the ocean was still twice of the present ocean (Knauth, 2005).Therefore, water-rock interactions took about 4 billion years tocleanse ocean perfectly for life where metazoans can readilysurvive. Therefore, landmass should not be small. To clean up toxicocean over 4 billion years, the landmass has to be huge. However,to make such a huge landmass above sea-level, the amount ofaccreted water by the ABEL Bombardment to generate the pri-mordial ocean becomes a critical constraint. The planet-widedepth of the primordial ocean needs to have been 4 � 1 km(Maruyama et al., 2013). If ocean was deeper than about 5 km, thelandmass could not appear above sea level. If it was less than 3 kmthick, plate tectonics could not initiate because of the absence ofhydration at mid-oceanic ridges. Either result would disrupt theHabitable Trinity, resulting in a failure to make the Earthhabitable.

3.7. Na-poor water

Modern cell cytoplasm is extremely poor in Naþ, whileconversely it is enriched in Kþ, and also enriched in PO4

3�. Thisindicates that the first cells is originated from highly reducedconditions that were highly depleted in Naþ ions and converselyenriched in Kþ, Zn2þ and Mn2þ. As Mulkidjanian et al. (2012)proposed, the birthplace of life would be such a site. The spe-cific example is a subduction-zone volcanic fumarole on land,instead of mid-oceanic ridge hydrothermal region. If the HadeanEarth was covered by KREEP basalt-bearing thick continentalcrust, and plate tectonics started, the mafic lower crustcomposed of KREEP gabbro would have produced extremely K-enriched arc magmas at subduction zones or metasomaticallymodified slab-melt by partial melting of a KREEP lower curst. Inthis sense, subduction-zone volcanoes satisfy this condition, andit should be noted that solidified KREEP basalt can also provide aK-rich environment.


Figure 8. The ABEL model. The Earth formed through two steps. The Earth was born as a dry rocky planet at 4.53 Ga. The Earth’s atmosphere and ocean were secondary accreted bythe ABEL Bombardment (4.37e4.20 Ga) (Maruyama and Ebisuzaki, 2017).


3.8. Highly diversified environments

The building blocks of life evolve from (1) combining theinorganic materials of CO2, H2O, N2 together with varieties ofnutrients, through (2) simple organic species of amino acids,ribose, nucleic acids, and simple proteins, which in turn lead to(3) enzymes, cycles, and ribozymes, then to a RNA-DNA world,and finally to (4) the first progenotes, or LUCAs. Membranes andcell walls must also develop during the earlier stages of thissequence, and finally all building blocks must get inserted intothe cell through a stepwise process. The possible pathways fromsimple inorganic matter to the first life with self-replicationfunctions, must pass through an immense number of chemicalreactions (Fig. 9).

To allow these reactions step-by-step to go forward, theinevitable first step is to synthesize numerous kinds of BBLs,requiring the different pH, pO2, temperature, salinity andchemical conditions related to the catalytic minerals, even


contrasting conditions, e.g., oxidized vs. reduced, or acidic vs.alkaline, at the same time at different place. Then, products haveto be merged one by one to generate more complex BBLs throughtime and environments. To enable these continuing and complexprocesses, the presence of a highly diversified surface environ-ment on the Hadean Earth is necessary, and it can provide thesole solution (Fig. 10 Left). Particularly, the appearance of hugelandmass enriched in nutrients is the most critical. If there is nolandmass, a “water-world” Earth with a homogeneous surfaceenvironment appears, in which case, there is no possibility tohave life (Fig. 10 Right). Highly diversified on-land environmentswith particularly localized and heterogeneous environments, arekey to the origin of life.

The highly diversified surface environments of the Hadean Earthare schematically illustrated in Fig.10 (left), which shows a bird-eyeview of 4.3 Ga Earth with large primordial continents, composed ofanorthosite (called PAN, MAN, and FAN), KREEP basalts filling incratered basins created by ABEL Bombardments, serpentinized Mg


Figure 9. The reaction network to generate the first life. The chart shows three basic functions of life, (1) metabolism, (2) self-replication, and (3) the formation of membranes. Thechemical reaction from inorganic matter to the first life involve innumerable complex organic components (building blocks of life). It remains unclear how many and whichpathways of reaction networks were used, and what crossings there were among the three categories of metabolism, self-replication and membrane creation, toward the birth ofthe first living organism.


suites (komatiites), newly formed andesite volcanic rocks and theirplutonic equivalents at subduction zones, U-ores associated withminerals such as schreibersite (Fe3P), and a variety of rock-formingminerals of Fe-oxides, Ni-Co alloys, Zn, Cu, Pb, Mn, native iron,oxides, sulfides, molybdenite (MoS2) and other key minerals togenerate the necessary metallic proteins. In addition to a variety ofrocks and minerals, topological diversity is also provided, such ashighlands, lowlands, tropical area, glaciated area, deserts, wetlands,lakes, swamps, and rivers on land. They can provide differentconditions according to site both physically and chemically, e.g.

Figure 10. Diversified earth and monotonous earth. Hadean Earth is thought to be a highmonotonous, with no diversified surface environment and hence, no possibility for the em


temperature, humidity, and chemical composition of lakes or rivers.Weathering, erosion, and transportation promoted by climate canprovide various nutrients to surrounding region with complexchemical composition.

3.9. Cyclic changes, such as day and night

Cyclic changes provide an important factor for maintaining lifecycles, as seen in the fundamental processes in which life is asso-ciatedwith periodic fluctuations (e.g. Hanczyc et al., 2003; Lambert,

ly diversified environment (left). If an ocean covers whole Earth (right), it would beergence of life.



2008). Periodic environmental change, such as temperature, pH,inorganic organic ions and anions, must have affected the earlieststeps of the life-forming process, e.g., low-temperature conditionsresult in regular crystallization of specific organic compounds,whereas high-temperature conditions promote random orientationof the crystalized organic compounds, with 60 �C as the criticaltransition temperature. This temperature fluctuation may berelated to the folding-unfolding of DNA, fragmentation-reconnection, and several steps for self-replication processes inthe RNA-DNA world. It is assumed that the cyclic changes in thesurrounding water chemistry would affect the fundamental pro-cesses of pre-biotic chemical evolution, and functions coded ingenes may provide a kind of “fossil” of environmental cyclicchanges.

One of the driving forces for this kind of periodicity is the self-rotation of the Earth (the day-night cycle), and another would bethe tidal effect of the Moon. The Hadean Moon was moving at aone-third closer orbit to the Earth with an orbital period of 5 hours(Benz et al., 1989; Canup and Asphaug, 2001), whichmeant that thetidal force was much stronger than at present and the tidal cycleswere also faster (Fig. 11).

4. The birthplace of life: evaluation of potential sites

The principal candidates for the birthplace of life were intro-duced in section 2. Herewe evaluate those birthplace models in thelight of the fundamental conditions required for the birthplace oflife that were described in section 3 (Table 2). We then assess themost probable model based on these requirements.

4.1. Mid-oceanic ridge: not birthplace of life, but a secondary origin

Among several birthplace hypotheses, Hadean MOR hypothesisseems to be supported bymajority of researchers. However, looking

Figure 11. Hadean surface environments of the Earth. Hadean surface environment experrotation of the Earth, and the faint young Sun.


into nine requirements listed in Table 2, it indicates that none of therequirements are met under the hydrothermal system at a MOR inthe Hadean Earth.

(1) Energy source; ionizing radiation (non-thermal energy) andthermal energy

The only energy source at MOR is the heat from underlyingmagma. To promote the chemical reaction between stable N2, H2O,and CO2, thermal energy supplied at MOR is not enough. Forexample, to make NH3 (needed to synthesize amino acids) from N2,temperatures over 500 �C are necessary to achieve the very highactivation energy level. However, it is extremely difficult to reachsuch a high temperature at a MOR. Even if it were possible, almostall BBLs would be broken at such a high temperature (Miller andBada, 1988). In other words, thermal energy, even if it can achievehigh enough temperatures, cannot contribute effectively to syn-thesize organic compounds.

(2) Supply of nutrients (K, REE, P, etc.)

The supply of nutrients, particularly coupled elements, such as Pand K, is critical to bear life. Hadean MOR magma is depleted inboth P and K (e.g. 1/400, Maruyama et al., 2013), because it wasproduced by higher degrees of partial melting of mantle peridotites(Takahashi, 1986; Maruyama et al., 2013). Therefore, MOR cannotsupply necessary elements in balance for BBLs like phosphoricacids, suggesting MORwas not suitable site to emerge life, or ratherworse in this regard.

(3) Supply of main life constituent elements (C, H, O, and N)

MOR is a highly aqueous environment, so there is no problem tosupply H and O. The biggest problem is the supply of N, because N is

ienced various types of cyclic phenomena, associated with a closer Moon, faster self-



the most difficult component to provide at MOR through magma-tism from underlying mantle. Basically, N is distributed in the pri-mordial atmosphere, and not in the solid Earth throughout theformation of primitive Earth. This is because there is no N-bearingmantle minerals. Therefore, Hadeanmantle lacked N. However, N isindispensable for the synthesis of amino acids, and there is no wayto synthesize amino acid and other complex organic compounds atMOR without N. If life has to originate at the MOR, there shouldhave a mechanism to enable continuous supply of N, but such amodel has not been proposed yet.

It could be argued that small amount of N dissolved from theatmosphere in the modern mantle, albeit this is not adequate forthe Hadean mantle. Originally, N cannot be incorporated in themantle minerals, so the supply of N from the mantle is impossible.The presence of N in the mantle is due to material circulationthrough plate subduction. The material circulation from trenchturbidites into the mantle could take in organics within clay min-erals produced on the surface environment. In the case of rare mica,when clay minerals dehydrate they generate K-mica, Na-mica andCa-mica that can survive under low temperature Phanerozoicmantle conditions. This process causes release of N from mantle,however it initiated only in the Phanerozoic through change insubduction zone geothermal gradients (Maruyama et al., 2014).Therefore, the minor presence of N in the mantle cannot be appliedto Hadean period. Also, minor ammonium can be observed in thedehydrated gas derived from MORBs, which is also after thePhanerozoic. In addition, the amount of such N is lower than theminimum values required to synthesize amino acids (e.g.Schlesinger and Miller, 1983; Cleaves et al., 2008). Therefore, thesupply of N at MOR is impossible to emerge life.

(4) Concentration of highly reduced gas

If MOR is the birthplace of life, the site must supply reducedgasses, such as NH3, HCN, KCN, CO, and CH4, to produce organiccompounds. The modern peridotite system at MOR does not pro-duce any reduced gasses because the amount of H2 is not enoughdue to the absence of komatiite, but Hadean MOR could be morereduced with the presence of komatiitic rocks (Russell and Hall,1997). In the Hadean, komatiite lava flows were erupted, wheremost sulfur escaped as gasses (Maruyama et al., 2013). Olivine-enriched (>60%) solidified lava flows offered an excellent mate-rial for the production of a reduced environment through H2 pro-duction, indicating MOR might be suitable site to give reducedgasses during the Hadean. However, gasses could not be adequatelyconcentrated to promote complex organic compounds becauseMOR hydrothermal vent is an open system. The concentration levelof reduced gas at MOR seems to be too diluted to promote reactionsleading to the building blocks of life. Hence, there is no possibility ofaccumulation of reduced gases at MOR, suggesting MOR cannot bea birthplace of life.

(5) Dry-wet cycle

MOR hydrothermal system completely fails to provide dry-wetenvironment to promote protein-forming reactions (polymeriza-tion) through dehydration-hydration cycle (e.g. Miller and Bada,1988; Deamer and Georgiou, 2015). The concept of a dry-wet cy-cle is a classic but basic requirement for the emergence of life aspointed out by Oparin (1924, 1957), Dyson (1982), Deamer (1997),Damer and Deamer (2015) and others. MOR hydrothermal systemcannot provide this important cyclic nature, thus it is impossible tobe the birthplace of life.


(6) Non-toxic water environments (less salt, less heavymetals, andneutral pH)

Hadean primordial ocean was too toxic; (1) a high salinity over5e10 times of present salinity, (2) super-acidic like pH< 0.1, and (3)ultra-enriched in heavy metals such as Fe, Mn, Mg, Cu, Zn, Pb, Mo,and Hg (e.g., Maruyama et al., 2013). MOR is, hence, underlain by atoxic ocean, therefore life cannot be born in such an environment.Eventually, life could enter an ocean to live, however, it is assumedafter Archean or more effectively after 635 Ma when salinity wasdown to double of present (Saito et al., submitted). Thus, our oceanhas not been a mother of life, nor the place of birth.

(7) Na-poor water

Hadean MOR environment is enriched in Na and nearly devoidof K, indicating a contrastingly opposite chemistry to cytoplasm oflife. It means there is no chance for life to emerge at Hadeankomatiitic MOR.

(8) Highly diversified environments

MOR is located as deep as 2.5 km below sea-level at present, andpresumably 3.1 km in the Precambrian, thus totally covered bymonotonous ocean, indicating no possibility of diversified envi-ronments around MOR since the middle Hadean. To producenumerous kinds of BBLs, even contrasting conditions, e.g., oxidizedvs. reduced, or acidic vs. alkaline, have to be provided to proceed toa series of chemical reactions. MOR in an ocean cannot meet thiscondition.

(9) Cyclic nature

Cyclic nature means the repetition of rising and lowering oftemperature, wet and dry conditions, and cyclic change ofcomposition of atmosphere or water. MOR is in open sea wherecyclic nature cannot bemaintained basically, due to free diffusion ofmaterial, constant and 100% moisturization and stable tempera-ture, suggesting no chance for life to emerge.

(10)Result: MOR is not birthplace, but a secondary site for life

Considering the nine requirements mentioned in this study,MOR cannot be the birthplace of life. Some workers invoke MORwith catalysts that can promote organic synthesis, such as FeS/FeS2,or other transition metal sulfides. There are some reports these caneven fix N2 (e.g. Schoonen and Xu, 2001; Dörr et al., 2003), thoughthere is no conclusive evidence. However, such a discussion isbasically limited to a few products like FeS. Birthplace shouldsupply numerous kinds of BBLs. Therefore, it is difficult to say thatMOR is the site where life could emerge because only some BBLscould be produced. Birthplace must produce all necessary productsto emerge life.

On the other hand, it is obvious that ecosystem has been presentat MOR, and chemo-autotrophic hyperthermophiles and meta-zoans are confirmed. In particular, hyperthermophile is known toappear close to the root of the phylogenetic tree (e.g. Martin andRussell, 2003), which preserves the earlier nature of micro-organisms. Microbes similar to methanogen has been alsoconfirmed at 3.5 Ga MOR (Ueno et al., 2001). Those facts indicatehyperthermophile entered MOR environment in early stage of theEarth’s history as well as methanogen. MOR is a stable



environmental domain to guarantee nearly constant temperatureand geochemical characters since the operation of plate tectonicsover 4.0 billion years. If there is no environmental change, life donot need to evolve. Therefore, it is nowonder that micro-organismsof MOR remain as relatively primitive biological characters,although they are not the primordial ones. MOR can be a trans-migrant site for life to survive in spite of the extreme environment,but it is not the birthplace of life.

4.2. Panspermia, neo-panspermia and mars origin

The fundamental problem of the Universe origin hypothesis(Panspermia, Neo-Panspermia, and Mars origin) is not explainingthe process or mechanism to emerge life. Panspermia and Marsorigin hypothesis clearly suggests that life was not born on theEarth, but lacked the explanation about when and how life couldemerge in the Universe, and how life could survive in the Universeduring the journey or the shock of the impact when they reached tothe Earth, or how they evolved on the Earth after the arrival. AsNeo-panspermiamodel explains, even if key substances, e.g. RNA orDNA, were delivered from the Universe, there is no proof for theemergence of first life. We are seeking clues on the birth of first lifefrom these BBLs.

For the sake of argument, it can be assumed that life came fromoutside of the Earth, like Mars or exoplanet. In such case, life musttravel with all other organisms forming their ecosystem, because

Figure 12. The solar system and materials from outside of the Earth. (A) Schematic illustrati2e5 AU. Also, comets come near to Earth periodically. (B) The impact of the meteor bombarebound by KREEP II basalts, which progress gradually over millions of years as mantle urebound scenario is applicable regardless of the size of impacting asteroid. (C) Cosmic dust coburned in upper atmosphere due to high energy particle radiation. Any organic molecules


life cannot survive with only one species. If life had come from theother planet, such ecosystem must fit to the Earth’s environmentwhen they migrate to the Earth. There are so many conditions forlife to survive, e.g. atmospheric composition such as O2 and CO2,oceanic pH, and the most important thing is food. Such a set ofcoincidences for all necessary conditions is almost impossible. TheEarth’s ecosystem evolved with terrestrial environment over time,which is co-evolution between life and earth and being applicablesince prebiotic stage of the emergence of life. Therefore, it is highlyunlikely that transported ecosystem fitted to Hadean environment.

However, universe origin hypothesis is favored by some re-searchers. We therefore explain what happens when material isdelivered to the Earth from the outer space. Fig. 12 is a schematicillustration of asteroid bombardment on the Earth. An exceptionallylarge asteroid that could hit the Earth is estimated to be about1000 km in diameter (Fig. 12B), which is equivalent to the size ofCeres in the asteroid belt. This sized asteroid can cause the for-mation of a crater with one-order-of-magnitude larger diameterimmediately after its impact. The temperature induced by thecollision will rise to more than 20,000 K (Davies, 1972; Hiesingerand Head, 2006), which can vaporize even the asteroid itself. Atthe same time, a similar mass of the solid Earth will turn to gas,whichwill be enriched in oxygen bymore than 50mol%, suggestingit would oxidize the primordial atmosphere. For example, the well-known Meteor Crater in Arizona (about 1.2e1.5 km in diameter)was formed by the impact of iron meteorite with diameter of

on of the solar system within 5 AU. Meteors come to the Earth from the asteroid belt atrdment is shown schematically. The excavated impact crater gets filled during mantlepwelling leads to de-compressional melting (Maruyama et al., 2018). Such a tectonicntaining organic molecules cannot reach to the surface of the Earth because the dust isin the cosmic dust turn to carbon.



20e30 m. However, the bulk of this iron meteorite evaporated andlittle remained around the impact crater. Even if the asteroid hadcontained volatiles (water), they would have evaporated due to theheat by the impact, which would cause a near-instantaneous vol-ume increase (ca. 1000 times) due to phase change from water togas. Likewise, organic matter, such as amino-acids, purine, andnucleotides contained in meteorite, would all have turned intoinorganic gas. Evaporated gas will diffuse and oxidize in the at-mosphere, so that nothing but the crater would be left after theimpact event. Even in situations that the ground preserves solidmeteorite fragments, containing organic molecules, these com-pounds would never come out from inside of meteorite sponta-neously to enter the ocean or atmosphere. Eventually, they wouldbe buried by sediments thereby preventing them from beingreused on the surface to constitute BBLs.

What about cosmic dust or ice composed of or containingorganic matter that is thought to be delivered from the space to thesurface of the Earth? Planetary scientists have long believed thatthe influx of organic matter in icy dust has been nearly negligibleever since the Earth originated in the earliest Hadean, and morespecifically, after the end of the heavy bombardment (the ABELBombardment in our model). Though Frank et al. (1986) proposed ahighly controversial hypothesis that an influx of small comets withorganic matter enters into the Earth’s upper atmosphere at a rate of1012 kg/yr, which would equal to the total volume of atmosphere ifit continued over 5 � 106 yr. However, this suggestion was rejectedby Dessler (1991) who pointed out both theoretical and observa-tional problems with such an immense flux of icy comets enteringEarth’s upper atmosphere. If the Frank hypothesis would be correct,Earth’s past sea-level changes would record the effects. However,there is no consistent geological evidence for such an influence.Wasson and Kyte (1987) calculated average deposition rate of comicflux as 9 � 3 ng Ir cm�2 Ma�1 on the basis of the Ir abundance ofPacific deep-sea sediments deposited at 33e67 Ma, except for K/Tboundary clays. Assuming a chondrite/ice ratio of 0.2, the ice fluxcan be estimated to be 2500 times smaller than that proposed byFrank et al. (1986). Thus, the geologic evidence preserved in deep-sea sediments does not support the idea that organic matter couldhave been continuously transported to Earth’s surface from theouter space over the past 4.0 Ga.

It is possible that cosmic dust can be delivered to the planets ofInner zone of the solar system periodically by comets, as exem-plified by the Halley Comet in 1986 imparted icy dust from its longtail over periods lasting from a few days to a month depending onthe orbital traces (Fig. 12A). What would be the fate of such dustscontaining ice and organic matter? Once such cosmic dust comesinto Earth’s upper atmosphere of the Earth, i.e. the ionosphere,temperatures will rise up due to high-energy particles. Dependingon the kind of influx materials, temperatures can reach up to2000 �C. Therefore, cosmic dust cannot maintain any organicmolecules under such extremely high temperatures because theorganic compounds would turn to be graphite. Any ice wouldevaporate and be blown away to the outer solar system (Fig. 12C).Therefore, this idea is inconsistent with both simple physics and thegeological evidence.

On the other hand, the idea of Mars-origin appear to have anadvantage, particularly from the evidence of “microbe” reportedfrom the ALH84001, as described in section 2. Actually, Mars mighthave possibility to bear life, as tested by the nine requirementslisted up in this paper (Table 2). The history of Mars and Earthshows close resemblance, and the Martian surface environmentexperienced similar evolution with Earth (e.g. Dohm et al., 2018).Mars is hypothesized to have Earth-like habitable trinity, and therewas possibility to meet all nine requirements in the past. However,complex organic matter or biosignature has not yet been


discovered on Mars even after investigations by Mars rover, Curi-osity (Ming et al., 2014; Freissinet et al., 2015), which indicates thatlife was not born on Mars, although the listed requirements werefulfilled.

4.3. Island arc volcanoes: hydrothermal field

Image of the environment of the birthplace of life described inthis model (Mulkidjanian et al., 2012) reflects the actual geologicalsite of Earth as well as the nuclear geyser model. The model of on-land hydrothermal field suggested good factors such as the chem-ical composition of cytoplasm, and the specific site to sustainhydration-dehydration process. However, it still lacked thecomprehensiveness to elucidate the birthplace. Particularly,absence of the energy source to raise energy density is critical. Also,their explanation does not include the possibility of highly reducedenvironment to produce HCN, CH4, H2, and NH3 for synthesis ofbasic BBLs. Therefore, this model is still insufficient to discuss abirthplace.

4.4. Geyser system driven by natural reactor with sufficient energydensity: most probable site for the birth of life

Nuclear Geyser model is only one hypothesis that can meet allnine requirements listed in Table 2. One of the most critical con-ditions is energy density to promote prebiotic chemical reactionbetween thermodynamically stable substances such as N2, H2O,and CO2. As shown in Fig. 13, the Sun’s energy is not enough topromote chemical reactions to produce important BBLs that requirehigh activation energy levels, indicating that life cannot emerge onthe surface of the Earth only with the Sun. Only one solution tomake continuous chemical reaction on Hadean Earth is the pres-ence of natural nuclear reactor to provide abundant high energyparticles such as aqueous electron to make complex organic mol-ecules from inorganic, which can easily clear energy uphill problem(Fig. 6). As Fig. 13 shows, the threshold value of energy density toproceed the prebiotic chemical evolution from inorganic com-pounds up to simple peptides is above 10�2 W/cm2 far strongerthan Hadean Sun radiation to the Earth. Even hydrothermal ventranges of 10�3e10�4 W/cm2 about one to two order of magnitudelower than the threshold value. Although it depends on the size ofthe reactor, energy density at 1m away from the core of nuclearreactor ranges of 10þ1e10�2 W/cm2 offering a good value to syn-thesize BBLs. If material is too close to the nuclear reactor, it isbroken, however, material is located at an ideal distance, it effec-tively involves in chemical reaction. Therefore, natural nuclearreactor plays the most important role to promote chemical reactionto produce BBLs.

However, the presence of nuclear reactor itself is not sufficientto lead to the emergence of life. Combination between a geyser andnatural nuclear reactor construct the perfect system that wouldmeet several critical conditions to bear life. The advantages of nu-clear geyser system are as follows. (1) Formation of highly reducedvolatiles such as H2, CO, CH4, NH3 and even HCN through water-rock interaction between wall rocks and inflow of surface waterinto the caves with the help of ionizing radiation by natural nuclearreactor, in spite of oxidized atmospheric composition of the surfaceenvironment (Fig. 5). (2) The reduced gasses generated areconcentrated on the ceilings of geyser cave, which maintains thereduced local environment. (3) With the flow of water into geysercave, reduced gas, high energy particles, intermediate activatedorganic matters, and other products react among one anotherthrough ionizing radiation to form more complex organic com-pounds, such as amino-acids and peptides can be progressing withincreasing distance from the natural reactor. (4) Periodic splash of



geyser system caused by phase change of water/vapor 1:1000,brings BBLs to the surface to be exposed to oxidizing environment.(5) In a small lake on the surface (Darwin’s warm little ponds), wet-dry cycle would polymerize amino-acids to proteins and finally toRNA or form membranes through evaporation by strong tidalforces. The most fruitful water-site for life forms was lacustrineenvironment on primordial continent, such as lakes, rivers, wetlands like swamps (Monnard and Deamer, 2002), which was pro-vided through global hydrological cycle driven by climate system(Maruyama et al., 2013). The materials produced on the surfaceoxidized environment are then brought down into the geyser caveagain in the process of material circulation. (6) Inside of geyserlacks high-temperature condition above 100 �C, because of periodiceruption of boiling water and vapor. Therefore, nuclear geysersystem would prevent the synthesized RNA and DNA from beingdestroyed, which provides unique characteristics as a birthplace.Also, periodic splashing sustains cyclic nature within the nucleargeyser system, which can be advantageous to change the waterchemistry, because solubility of inorganic ions, anions and organicsdepends on temperature. This would help the evolution from RNAto DNA world.

Generally, it is assumed that life cannot live with radiationbecause the decay of U235 has been regarded to be deadly for life,although there are many radio-resistant bacteria even on modernEarth, such as Deinococcus radiodurans (Makarova et al., 2001;Rothschild and Mancinelli, 2001; Ishino and Narumi, 2015). Therecently discovered bacteria, Rubrobacter radiotolerans can surviveunder 4000 times stronger radiation than the lethal level of humanbeing, that is 400 times stronger than the critical level of Bacillus

Figure 13. Energy densities and the threshold value needed to resolve the energy uphill prothe energy level from the Hadean and modern Sun is insufficient to overcome the energy


coli (Saito, 2007). Its resistance level is twice than that of D. radi-odurans. The presence of this kind of life suggests that life hasexperienced radioactive environment and produced the survivalprogram in DNA.

Nuclear Geyser model is the first proposal which combines ra-diation physics, geological validity on Hadean Earth, and the birthof life with a coherent explanation of its process from inorganic tofirst life. At present, nuclear geysermodel has no rebuttal evidenceswith the listed nine requirements (Table 2), although further in-vestigations in future might lead to the refinement or rebuttal ofthis model.

5. Discussion

5.1. Significance of chemical oversaturation in the incubator as acradle of life

Each of the listed requirements in Table 2 is significant whenwediscuss the emergence of the first life. If even one of the re-quirements cannot be satisfied, life would not commence on Earth.However, in addition to meeting all the nine conditions, there isanother important collateral condition to be emphasized, which ischemically oversaturated condition For example, although thepresence of a reducing gas, such as H2 and HCN, is a necessaryrequirement, its mere presence is not sufficient. The reducing gasmust be concentrated in order to form organic molecules. Presenceitself cannot lead to the emergence of life, thus, the incubator of thefirst life needs to provide chemically oversaturated conditions. Thesame principle can be applied to water-rock interactions. The wall

blem for the origin of life. The horizontal bold red line is the threshold value. Note thatuphill problem (the activation energy).



rocks of the inner geyser system, such as anorthosite, komatiite andKREEP basalts, would also have various kinds of secondarymineralsbecause of water-rock interactions. For example, magnetite, FeeNialloys, pentlandite, brucite, serpentine minerals, and pyrite aresecondary minerals that form in serpentinite: Fe-S, (Zn, Fe)S, MoS,PbS, and TiO2 form in KREEP basalt; and carbonates and CaeAlsilicates form in anorthosite. These minerals play a role as catalyticminerals that produce metallic proteins and enzymes to poly-merize more complex BBLs. However, to yield these secondaryminerals from their host rocks (serpentinite, KREEP basalts, andanorthosite), they must contain the necessary components atgreater than thermodynamically oversaturated levels throughwater-rock interaction. The mere presence of these components ofthe secondary minerals in the host rocks is not sufficient, andoversaturation is required.

5.2. Debate on the birthplace of life: conditions for life’s birth differfrom those of its evolution

What we need to emphasize here is that the conditions for thebirth of life are different from those of its subsequent evolution. Inother words, the nine requirements listed in Table 2 are notnecessarily met in life’s evolutional stage. Once life was initiatedwith necessary functions such as metabolism, membrane, and self-replication, the situation is quite different. The emergent life wouldthen be able to survive through adaptive evolution even in extremeenvironments like a MOR hydrothermal vent. Significant point is todistinguish the origin and the evolution when we discuss life. “Theorigin of life” is the research for creation of life from abiotic sub-stance, while “the evolution of life” is to discuss that how life couldadapt to different environmental conditions including changes inecosystem. Therefore, nine requirements proposed in this paper isonly applicable to the point of origin, not to the evolutional stage.

In addition, the site to meet all nine requirements is in very rarecircumstances even on Hadean earth. Probably both geysers anduranium ores are ubiquitous in Hadean as we stated in earliersection. However, it is not easy to clear listed conditions one by one.Even if geyser could be combined with uranium ore as a naturalreactor, it will be another difficult condition to have necessaryHadean rocks within a nuclear geyser to form necessary BBLs. Also,it could be difficult to have an ideal underground space to promoteprebiotic chemical reactions with suitable material circulation.These collateral environmental conditions make the birthplacemore complicated. Considering these difficulties, the places thatmeets all the nine requirements cannot be many. It might be onlyone site on the Earth.

Generally, it has been vaguely considered that the first life wasborn everywhere on the Hadean Earth if the conditions are right;specifically, the presence of water and reduced atmosphere. Theaim of this paper is to point out that there are more requirements tosatisfy the birthplace of life, and the birthplace could be only onepoint on an entire Earth, like the origin of human being along theAfrican Rift Valley.

5.3. New tree of life derived from geology: what is life living aroundHadean hydrothermal vent at mid-oceanic ridge?

In the Hadean, plate tectonics destroyed all primordial conti-nents and carried them into deepermantle by tectonic erosionwithtime (Maruyama et al., 2013; Maruyama and Ebisuzaki, 2017). As aresult, Hadean continents as mother of life must have disappearedfrom the surface, whereas a number of intra-oceanic island arcsbegan forming. Primitive life lost the place to live due to disap-pearance of almost all continent by the end of Hadean at 4.0 Ga.Very limited species could survive on small island arcs. On the other


hand, some life is assumed to have adapted to the deep oceanicenvironment at the spreading ocean.

From such Hadean history based on geological evidence, inaddition to phylogenic tree derived from biology, we propose a newtree of life. As stated in a previous section, the key to the origin andevolution of life is the environmental change. In other words, anenvironment controls both origin and evolution, which is alsonoted by Charles Darwin; “no environmental change, no evolu-tion”. Considering the tree of life based on environmental con-straints, tree should reflect the habitat of life in terms of increasingpO2 through time.

Fig. 14 shows such a new tree of life. First prokaryote, evolvedfrom proto-life was regarded to be born on land centering on nu-clear geyser system. With time, they migrated to other sites on theEarth and evolve to adapt different environmental condition. Someof them remained on land, where the situation was significantlytough due to loss of primordial continent and exposed to outerspace of the Earth to suffer from the influx of UV and GCR. Such lifeshould have gone through dramatic evolutionary process to sur-vive. On the other hand, some other species migrated into hydro-thermal vent which is quite stable and unchanging environmentthrough time. The bottom of ocean is protected from UV, GCR, orenvironmental changes caused by geologic activities.

However, as we explained, Hadean ocean was too toxic and lifecould not survive in such environment. If so, how life could come tolive in deep sea hydrothermal vent? The key is life cycle of mid-oceanic ridge as schematically shown in Fig. 15. Initially, mid-oceanic ridge appears on land, like African Rift Valley (Fig. 15a andd). In other word, it is not “mid-oceanic ridge”, but the rift on thecontinent. Rift is formed through the upwelling of mantle plumes.Curtain-like upwelling is generated by the connection of two plumesrising from 410 km depth of upper mantle, where decompressionmelting through mantle upwelling provides magma in divergentregion to cause the ridge push force. This is the process to form therift on the continent (Fig.15a and d). Continuous uplifting and supplyof magma forms larger rift system where a number of normal faultsdevelop, and chasm spreads and expands to both sides of the axis ofthe rift (Fig. 15b and e). Uplift activity gradually widens and deepensthe chasm to fill it with clear water by rainfall where primitive lifecould migrate from nuclear geyser region along the ridge axis on thesame continent. That life could utilize both magmatic heat energyfrom the Earth’s interior and clean water, then adapt to this envi-ronment, which should have been different from geyser environ-ment. With time, the chasm becomes much larger and deeper toresult in breaking of continent. Finally, toxic ocean starts to fill thechasm, probably it would start with the mixing between toxic oceanand clean water, then filled by full toxic ocean at the end (Fig. 15c, f,g). However, primitive life, migrated from nuclear geyser system,could survive within hydrothermal vent system where boiled cleanwater is supplied continuously. In this regard, MOR is very uniquesite, where gushing boiled clean water is continuously supplied.Through boiling of saline water, relatively dense brine sinks downwhile fresh boiledwater is released fromMOR. Therefore, immediatevicinity of MOR provides non-toxic environment in spite of thebottom of a toxic ocean. In addition, MOR is a very stable environ-ment since Hadean time, as opposed to the surface environmentwhich underwent dramatic changes through time, e.g. snowballEarth events in Hadean, gradual or rapid increase in density of at-mospheric oxygen, amalgamation and dispersion of continents.Therefore, migrant life in hydrothermal vent did not have to evolveor adapt to changing environment, suggesting the oldest type of lifecould survive there if they had migrated and adapted there duringthe Hadean.

In Hadean time, the surface environment was more reducing.Through the evolution of the Earth, environment has gotten


Figure 14. A new tree of life, derived from the combination of geologic perspective and phylogenetic tree of life. First life was born in the nuclear geyser system through three stepevolution, and evolved into two domains. One is microbes on-land, the other is microbes in water. On-land microbes were exposed to more severe environment, while microbes inwater enjoyed under stable environment.


oxidized, and since 600 Ma, reducing environment has almost losteven in ocean because about 10% of atmospheric oxygen is dis-solved into sea water and circulate down to the bottom of theocean. Therefore, pleasant environment for primitive life do notexist anymore excluding an exception of hydrothermal vents alongoceanic transform faults where serpentinization produces H2 tokeep extremely local reducing environment with moderate tem-perature, like Lost City.

5.4. Role of universe for the origin and evoluton of life on the earth

As another factor to force the environmental change is thechange in the outer space, which must be also emphasized here,because birth of life on the Earth may have been strongly influ-enced by collisions of galaxies. It is already established thatsnowball events occurred twice in the Earth history which accel-erate the evolution of life, e.g. first snowball was at 2.3e2.2 Gawhen life evolved from prokaryotes to eukaryotes, and second onewas at 0.8e0.5 Ga evolving into metazoas and plants, called theCambrian explosion. Both events correspond to starburst periods(Fig. 16). Although the records are lost on the Earth, the occurrenceof starburst in Hadean time is reported (Rocha-Pinto et al., 2000; de


la Fuente Marcos and de la Fuente Marcos, 2004), which suggestssnowball state appeared during the birth period of proto-life.

In the past, starburst occurred due to collision of a dwarf-galaxyagainst our galaxy, generated enormous amounts of galactic cosmicrays to form cloud leading snowball event (Kataoka et al., 2013,2014). This event extensively affected the earliest evolution ofproto-life on the Earth. Frequent oscillation of climate betweensuper-cold (�50 �C) and super-hot (þ50 �C), should have causedmass extinction repeatedly (Hoffman and Schrag, 2000, 2002).Close relationship between glaciation and space event has beengiving a new insight for mass extinction event. For example, massextinction occurred in the Phanerozoic, e.g., P/T boundary and K/Tboundary, in which new data suggests the collision of Dark Cloudagainst our solar system. This collisional event led similar climatechange as well as the case by starburst, although it might be orderof magnitude smaller than the snowball state (Nimura et al., 2016).

5.5. Complex science and falsifiability: significance of workinghypothesis to understand origin of life

A proposal of hypothesis is a necessary step in the complexityscience, especially for the case that a phenomenon cannot be easilyexpressed by the combination of formulae. Some workers consider


Figure 15. Life cycle of mid-oceanic ridge. (a) A continental rift appears on the land due to the upwelling of mantle plumes. (b) Continuous uplifting and the supply of magma formslarger rift system where a number of normal faults develop. A chasm spreads and expands to both sides of the axis of the rift. (c) Finally a continent breaks off. Hadean toxic oceanfills the chasm. (d) A continental rift appears on the land. Clean water by rainfalls fill the valley. (e) Rift systems widens and water fill in the valley. (f) A continent start to break off.Hadean toxic ocean floods into the valley. (g) A continent completely breaks up. Continental rift turns to mid-oceanic ridge.


that physics can explain all kind of phenomena, however, physics isone of tools to express phenomenon following assumptions.Complexity science represented by biology has numerous param-eters, therefore it is impossible to solve a system of equations inbiology like in physics or mathematics. To overcome this situation,hypothesis play a critical role to enable us to testify the model. Ahypothesis containing rebuttal evidences should be replaced bymore reasonable hypothesis, however, this process assists to makethe hypothesis more reasonable or get close to the truth.

In order to evaluate the birthplace of life, it is essential to un-derstand and base the arguments on scientific philosophy, specif-ically in the case of complex and interdisciplinary branches ofscience like biology and geology. Falsifiability, proposed byAustrian-British science philosopher Karl Popper (1902e1994), isparticularly important. Most laws in biology are empirical, based ona number of observations. A number of observations cannot verifyuniversal generalization. For example, there is the statement that“all crows are black” as an empirical law or working hypothesis,however it is not possible to demonstrate to be true, because even if100th crows are black, the 101st crow can be white; similarly, if1000th crows are black the 1001st crow can be white. Therefore,“all crows are black” cannot be demonstrated. This is a problem ofinduction, but this statement can be testified by the discovery ofwhite crow. Such testability, e.g. falsifiability, is critical to distin-guish scientific from unscientific. Popper stressed the significance


of falsifiability (Popper, 1959). What unfalsifiable is regarded un-scientific, then practice to explain unfalsifiable statement, hy-pothesis, or theory to be scientifically true is pseudoscience.

At present, it is known that the color of crows is controlled by agene anomaly, and white crows are known as Albino. Like thisexample, elucidation of mechanism lays the principle to explainvariousphenomena. Biological science is pivotedon severalworkinghypotheses, and has progressed much to understand the differentintriguing phenomena through time. To systematize biology, theoryor working hypothesis has to be falsifiable or testable as statedabove. Even if hypothesis is gained by induction, falsifiability cangives the way to the authentic achievement to unravel the truth,including themysteryof theoriginof life andbirthplaceof life.Whenthe birthplace of life at MOR was proposed, Miller and Bada (1988)opposed the idea of MOR because of no chance of dry/wet cycle.This is one of the typical examples to improve hypothesis withfalsifiability. One negative evidence can deny the hypothesis, whichis inevitable process for complex science.

As stated in this paper, geological perspective will be morepowerful tool to unravel the origin and evolution of life. Lifeevolved to respond to the environmental changes, and environ-mental evidence is accessible through world geology. Moreover,geological perspective can be applied to other planetary bodiesincluding exo-planets, which will provide the possibility to discussAstrobiology more in details.


Figure 16. Relationship between events in the universe and the life’s origin and evolution. At the top of the chart, three starburst periods caused by galaxy collisions are shown: (I)middle Hadean, (II) 2.3e2.2 Ga, and (III) 0.8e0.5 Ga in our Milky-Way Galaxy. Starburst causes Snowball periods to cause rapid evolution of life through extensive mass extinction.Another critical event for life is the state of geomagnetism. Strong geomagnetism protects the surface environment for life. If weak geomagnetism and universal event is combined,Earth’s life is severely affected.


6. Conclusion

From a comprehensive review of previous research on the originof life and birthplace of life, we picked up nine requirements to befulfilled for the birthplace of life: (1) an energy source (ionizingradiation and thermal energy); (2) a supply of nutrients (P, K, REE,etc.); (3) a supply of life-constituting major elements; (4) a highconcentration of reduced gases such as CH4, HCN and NH3; (5) dry-wet cycles to create membranes and polymerize RNA; (6) a non-toxic aqueous environment; (7) Na-poor water; (8) highly diversi-fied environments, and (9) cyclic conditions, such as day-to-night,hot-to-cold etc.

Based on these nine requirements, we evaluated previouslyproposed hypotheses for the birth place of life such as a deep-seahydrothermal system, Neo-panspermia model, and others. Wepropose that Nuclear Geyser model is the most plausible scenarioas a birthplace of first life. Geyser system combined with uraniumore as a natural nuclear reactor could produce necessary material toform life through ionizing radiation and material circulation.

Acknowledgements

This research was supported by MEXT KAKENHI: Grant-in-Aidfor Scientific Research on Innovative Areas, Grant Numbers26106002, 26106004, 26106006: Hadean Bioscience, and also bythe Ministry of Education and Science of the Russian Federation,Project No. 14.Y26.31.0018. The authors thank Ms. Reiko Hattori fortechnical assistance in completing this paper and Prof. Victor R.Baker, University of Arizona, for comments and help with some ofthewriting. The illustrations were prepared with the support of Ms.Shio Watanabe.


References

Abe, Y., Matsui, T., 1986. Early evolution of the Earth: accretion, atmosphere for-mation, and thermal history. Journal of Geophysical Research 91, E291eE302.

Adam, Z.R., 2016. Temperature oscillations near natural nuclear reactor cores andthe potential for prebiotic oligomer synthesis. Origins of Life and Evolution ofthe Biosphere 46, 171e187.

Arai, T., Maruyama, S., 2017. Formation of anorthosite on the Moon through magmaocean fractional crystallization. Geoscience Frontiers 8, 299e308.

Arrhenius, S., 1908. Worlds in the Making: the Evolution of the Universe. Harper.Bada, J.L., Lazcano, A., 2003. Prebiotic soup e revisiting the miller experiment.

Science 300, 745e746.Baross, J.A., Hoffman, S.E., 1985. Submarine hydrothermal vents and associated

gradient environments as sites for the origin and evolution of life. Origins of Life15, 327e345.

Bell, E.A., Boehnke, P., Harrison, T.M., Mao, W.L., 2015. Potentially biogenic carbonpreserved in a 4.1 billion-year-old zircon. Proceedings of the National Academyof Sciences 112, 14518e14521.

Benz, W., Cameron, A.G.W., Melosh, H.J., 1989. The origin of the Moon and thesingle-impact hypothesis III. Icarus 81, 113e131.

Bodu, R., Bouzigues, N., Moin, N., Pfiffelman, J.P., 1971. Sur l’existence d’anomaliesisotopiques rencontrées dans l’uranium du Gabon. Comptes Rendus De L Aca-demie Des Sciences Paris 275, 1731-1731.

Canup, R.M., Asphaug, E., 2001. Origin of the Moon in a giant impact near the end ofthe, Earth’s formation. Nature 412, 708e712.

Charlou, J.L., Donval, J.P., Fouquet, Y., Jean-Baptiste, P., Holm, N., 2002. Geochemistryof high H2 and CH4 vent fluids issuing from ultramafic rocks at the Rainbowhydrothermal field (36�140N, MAR). Chemical Geology 191, 345e359.

Cleaves, H.J., Chalmers, J.H., Lazcano, A., Miller, S.L., Bada, J.L., 2008. A reassessmentof prebiotic organic synthesis in neutral planetary atmospheres. Origins of Lifeand Evolution of the Biosphere 38, 105e115.

Corliss, J.B., Baross, J.A., Hoffman, S.E., 1981. An hypothesis concerning the rela-tionship between submarine hot springs and the origin of life on Earth. Oce-anologica Acta 4, 59e69.

Crick, F.H.C., Orgel, L.E., 1973. Directed panspermia. Icarus 19, 341e346.Damer, B., Deamer, D., 2015. Coupled phases and combinatorial selection in fluc-

tuating hydrothermal pools: a scenario to guide experimental approaches tothe origin of cellular life. Life 5, 872.

Darwin, C., 1859. On the Origin of Species. John Murray, Albemable Street, London.Davies, G.F., 1972. Equations of state and phase equiribria of stishovite and a coesite-

like phase from shock-wave and other data. Journal of Geophysical Research 77,4920e4933.


http://refhub.elsevier.com/S1674-9871(18)30212-3/sref1

























































de la Fuente Marcos, R., de la Fuente Marcos, C., 2004. On the correlation betweenthe recent star formation rate in the Solar Neighbourhood and the glaciationperiod record on Earth. New Astronomy 10, 53e66.

Deamer, D.W., 1997. The first living systems: a bioenergetic perspective. Microbi-ology and Molecular Biology Reviews 61, 239e261.

Deamer, D., 2016. Membranes and the origin of life: a century of conjecture. Journalof Molecular Evolution 83, 159e168.

Deamer, D.W., Georgiou, C.D., 2015. Hydrothermal conditions and the origin ofcellular life. Astrobiology 15, 1091e1095.

Deming, J.W., Baross, J.A., 1993. Deep-sea smokers: windows to a subsurfacebiosphere. Geochimica et Cosmochimica Acta 57, 3219e3230.

Dessler, A.J., 1991. The small-comet hypothesis. Reviews of Geophysics 29, 355e382.Dohm, J.M., Maruyama, S., 2015. Habitable trinity. Geoscience Frontiers 6,

95e101.Dohm, J.M., Maruyama, S., Kido, M., Baker, V.R., 2018. A possible anorthositic

continent of early Mars and the role of planetary size for the inception of Earth-like life. Geoscience Frontiers 9, 1085e1098.

Doolittle, W.F., 1999. Phylogenetic classification and the universal tree. Science 284,2124e2128.

Dörr, M., Käßbohrer, J., Grunert, R., Kreisel, G., Brand, W.A., Werner, R.A.,Geilmann, H., Apfel, C., Robl, C., Weigand, W., 2003. A possible prebiotic for-mation of ammonia from dinitrogen on iron sulfide surfaces. AngewandteChemie International Edition 42, 1540e1543.

Dyson, F.J., 1982. A model for the origin of life. Journal of Molecular Evolution 18,344e350.

Ebisuzaki, T., Maruyama, S., 2017. Nuclear geyser model of the origin of life: drivingforce to promote the synthesis of building blocks of life. Geoscience Frontiers 8,275e298.

Fox, G., Stackebrandt, E., Hespell, R., Gibson, J., Maniloff, J., Dyer, T., Wolfe, R.,Balch, W., Tanner, R., Magrum, L., Zablen, L., Blakemore, R., Gupta, R., Bonen, L.,Lewis, B., Stahl, D., Luehrsen, K., Chen, K., Woese, C., 1980. The phylogeny ofprokaryotes. Science 209, 457e463.

Frank, L.A., Sigwarth, J.B., Craven, J.D., 1986. On the influx of small comets into theEarth’s upper atmosphere II. Interpretation. Geophysical Research Letters 13,307e310.

Freissinet, C., Glavin, D.P., Mahaffy, P.R., Miller, K.E., Eigenbrode, J.L., Summons, R.E.,Brunner, A.E., Buch, A., Szopa, C., Archer, P.D., Franz, H.B., Atreya, S.K.,Brinckerhoff, W.B., Cabane, M., Coll, P., Conrad, P.G., Des Marais, D.J.,Dworkin, J.P., Fairén, A.G., François, P., Grotzinger, J.P., Kashyap, S., Kate, I.L.,Leshin, L.A., Malespin, C.A., Martin, M.G., Martin-Torres, F.J., McAdam, A.C.,Ming, D.W., Navarro-González, R., Pavlov, A.A., Prats, B.D., Squyres, S.W.,Steele, A., Stern, J.C., Sumner, D.Y., Sutter, B., Zorzano, M.P., 2015. Organicmolecules in the sheepbed Mudstone, gale crater, Mars. Journal of GeophysicalResearch: Planets 120, 495e514.

Gauthier-Lafaye, F., Weber, F., 2003. Natural nuclear fission reactors: time con-straints for occurrence, and their relation to uranium and manganese depositsand to the evolution of the atmosphere. Precambrian Research 120, 81e100.

Gold, T.H., 1992. The deep, hot biosphere. Proceedings of the national Academy ofSciences USA 89, 6045e6049.

Hanczyc, M.M., Fujikawa, S.M., Szostak, J.W., 2003. Experimental models of primitivecellularcompartments: encapsulation, growth, anddivision. Science302, 618e622.

Hiesinger, H., Head, J.W., 2006. New views of lunar feoscience: an introduction andoverview. Reviews in Mineralogy and Geochemistry 60, 1e81.

Hoffman, P.F., Schrag, D.P., 2000. Snowball earth. Scientific American 282, 68e75.Hoffman, P.F., Schrag, D.P., 2002. The snowball Earth hypothesis: testing the limits

of global change. Terra Nova 14, 129e155.Hoyle, F., Wickramasinghe, N.C., 1999. Comets e a vehicle for panspermia. Astro-

physics and Space Science 268, 333e341.Ishino, Y., Narumi, I., 2015. DNA repair in hyperthermophilic and hyper-

radioresistant microorganisms. Current Opinion in Microbiology 25, 103e112.Jannasch, H.W., Mottl, M.J., 1985. Geomicrobiology of deep-sea hydrothermal vents.

Science 229, 717e725.Kataoka, R., Ebisuzaki, T., Miyahara, H., Maruyama, S., 2013. Snowball earth events

driven by starbursts of the Milky way galaxy. New Astronomy 21, 50e62.Kataoka, R., Ebisuzaki, T., Miyahara, H., Nimura, T., Tomida, T., Sato, T., Maruyama, S.,

2014. The Nebula Winter: the united view of the snowball Earth, mass ex-tinctions, and explosive evolution in the late Neoproterozoic and Cambrianperiods. Gondwana Research 25, 1153e1163.

Kelley, D.S., Karson, J.A., Blackman, D.K., Fruh-Green, G.L., Butterfield, D.A.,Lilley, M.D., Olson, E.J., Schrenk, M.O., Roe, K.K., Lebon, G.T., Rivizzigno, P.,the, A.T.S.P., 2001. An off-axis hydrothermal vent field near the Mid-AtlanticRidge at 30o N. Nature 412, 145e149.

Kelley, D.S., Karson, J.A., Früh-Green, G.L., Yoerger, D.R., Shank, T.M., Butterfield, D.A.,Hayes, J.M., Schrenk, M.O., Olson, E.J., Proskurowski, G., Jakuba, M., Bradley, A.,Larson, B., Ludwig, K., Glickson, D., Buckman, K., Bradley, A.S., Brazelton, W.J.,Roe, K., Elend, M.J., Delacour, A., Bernasconi, S.M., Lilley, M.D., Baross, J.A.,Summons, R.E., Sylva, S.P., 2005. A serpentinite-hosted ecosystem: the lost cityhydrothermal field. Science 307, 1428e1434.

Kirschvink, J.L., Weiss, B.P., 2003. Mars, panspermia, and origin of life: where did itall begin? Journal of Geography 112, 187e196.

Knauth, L.P., 2005. Temperature and salinity history of the Precambrian ocean:implications for the course of microbial evolution. Palaeogeography, Palae-oclimatology, Palaeoecology 219, 53e69.

Kuroda, P.K., 1956. On the nuclear physical stability of the uranium minerals. TheJournal of Chemical Physics 25, 781-781.


Lambert, J.-F., 2008. Adsorption and polymerization of amino acids on mineralsurfaces: a review. Origins of Life and Evolution of the Biosphere 38, 211e242.

Lancelot, J.R., Vitrac, A., Allegre, C.J., 1975. The Oklo natural reactor: age and evo-lution studies by UPb and RbSr systematics. Earth and Planetary Science Letters25, 189e196.

Levy, R.L., Grayson, M.A., Wolf, C.J., 1973. The organic analysis of the murchisonmeteorite. Geochimica et Cosmochimica Acta 37, 467e483.

Makarova, K.S., Aravind, L., Wolf, Y.I., Tatusov, R.L., Minton, K.W., Koonin, E.V.,Daly, M.J., 2001. Genome of the extremely radiation-resistant Bacterium Dein-ococcus radiodurans viewed from the perspective of comparative genomics.Microbiology and Molecular Biology Reviews 65, 44e79.

Martin, W., Russell, M.J., 2003. On the origins of cells: a hypothesis for the evolu-tionary transitions from abiotic geochemistry to chemoautotrophic pro-karyotes, and from prokaryotes to nucleated cells. Philosophical Transactions ofthe Royal Society of London Series B Biological Sciences 358, 59e83.

Maruyama, S., Ebisuzaki, T., 2017. Origin of the Earth: a proposal of new modelcalled ABEL. Geoscience Frontiers 8, 253e274.

Maruyama, S., Ikoma, M., Genda, H., Hirose, K., Yokoyama, T., Santosh, M., 2013. Thenaked planet Earth: most essential pre-requisite for the origin and evolution oflife. Geoscience Frontiers 4, 141e165.

Maruyama, S., Santosh, M., Azuma, S., 2018. Initiation of plate tectonics in theHadean: Eclogitization triggered by the ABEL Bombardment. Geoscience Fron-tiers 9, 1033e1048.

Maruyama, S., Sawaki, Y., Ebisuzaki, T., Ikoma, M., Omori, S., Komabayashi, T., 2014.Initiation of leaking Earth: an ultimate trigger of the Cambrian explosion.Gondwana Research 25, 910e944.

McDonough, W.F., Sun, S.S., 1995. The composition of the Earth. Chemical Geology120, 223e253.

McKay, D.S., Gibson, E.K., Thomas-Keprta, K.L., Vali, H., Romanek, C.S., Clemett, S.J.,Chillier, X.D.F., Maechling, C.R., Zare, R.N., 1996. Search for past life on Mars:possible relic biogenic activity in Martian meteorite ALH84001. Science 273,924e930.

Miller, S.L., 1953. A production of amino acids under possible primitive earth con-ditions. Science 117, 528e529.

Miller, S.L., Bada, J.L., 1988. Submarine hot springs and the origin of life. Nature 334,609e611.

Miller, S.L., Urey, H., 1959. Organic compound syntheis on the primitive Earth.Science 130, 245e251.

Ming, D.W., Archer, P.D., Glavin, D.P., Eigenbrode, J.L., Franz, H.B., Sutter, B.,Brunner, A.E., Stern, J.C., Freissinet, C., McAdam, A.C., Mahaffy, P.R., Cabane, M.,Coll, P., Campbell, J.L., Atreya, S.K., Niles, P.B., Bell, J.F., Bish, D.L.,Brinckerhoff, W.B., Buch, A., Conrad, P.G., Des Marais, D.J., Ehlmann, B.L.,Fairén, A.G., Farley, K., Flesch, G.J., Francois, P., Gellert, R., Grant, J.A.,Grotzinger, J.P., Gupta, S., Herkenhoff, K.E., Hurowitz, J.A., Leshin, L.A.,Lewis, K.W., McLennan, S.M., Miller, K.E., Moersch, J., Morris, R.V., Navarro-González, R., Pavlov, A.A., Perrett, G.M., Pradler, I., Squyres, S.W., Summons, R.E.,Steele, A., Stolper, E.M., Sumner, D.Y., Szopa, C., Teinturier, S., Trainer, M.G.,Treiman, A.H., Vaniman, D.T., Vasavada, A.R., Webster, C.R., Wray, J.J.,Yingst, R.A., 2014. Volatile and organic compositions of sedimentary rocks inYellowknife Bay, Gale crater, Mars. Science 343.

Monnard, P.A., Deamer, D.W., 2002. Membrane self-assembly processes: steps to-ward the first cellular life. The Anatomical Record 268, 196e207.

Mulkidjanian, A.Y., Bychkov, A.Y., Dibrova, D.V., Galperin, M.Y., Koonin, E.V., 2012.Origin of first cells at terrestrial, anoxic geothermal fields. Proceedings of theNational Academy of Sciences of the United States of America 109, E821eE830.

Ndongo, A., Guiraud, M., Vennin, E., Mbina, M., Buoncristiani, J.-F., Thomazo, C.,Flotté, N., 2016. Control of fluid-pressure on early deformation structures in thePaleoproterozoic extensional Franceville Basin (SE Gabon). PrecambrianResearch 277, 1e25.

Neuilly, M., Nief, G., Vendryes, G., Yvon, J., Bussac, J., Frejacqu, C., 1972. Sur l’exstencedans un passe recule d’une reaction en chaine naturelle de fission, dans legisement d’uranium d’Oklo (Gabon). C.R. Academy of Science, Paris 275,1847e1849.

Nimura, T., Ebisuzaki, T., Maruyama, S., 2016. End-cretaceous cooling and massextinction driven by a dark cloud encounter. Gondwana Research 37, 301e307.

Nuckley, D.J., Jinks, R.N., Battelle, B.A., Herzog, E.D., Kass, L., Renninger, G.H.,Chamberlain, S.C., 1996. Retinal anatomy of a new species of Bresiliid shrimp:from a hydrothermal vent field on the mid-Atlantic ridge. The BiologicalBulletin 190, 98e110.

Ochiai, E., 2008. Bioinorganic Chemistry. Academic Press, New York.Oparin, A.I., 1924. Proiskhozhdenic Zhizny. Izd. Moskovski Rabochii, Moscow.Oparin, A.I., 1957. The Origin of Life on the Earth. Academic Press, New York.Pasek, M.A., 2015. Phosphorus as a lunar volatile. Icarus 255, 18e23.Pizzarello, S., Huang, Y., Becker, L., Poreda, R.J., Nieman, R.A., Cooper, G.,

Williams, M., 2001. The organic content of the Tagish Lake meteorite. Science293, 2236e2239.

Popper, K., 1959. The Logic of Scientific Discovery. Hutchinson & Co.Rocha-Pinto, H.J., Maciel, W.J., Scalo, J., Flynn, C., 2000. Chemical enrichment and

star formation in the Milky Way disk I. Sample description and chromosphericage-metallicity relation. Astronomy and Astrophysics 358, 850e868.

Rothschild, L.J., Mancinelli, R.L., 2001. Life in extreme environments. Nature 409,1092e1101.

Russell, M.J., Daniel, R.M., Hall, A.J., Sherringham, J.A., 1994. A hydrothermallyprecipitated catalytic iron sulphide membrane as a first step toward life. Journalof Molecular Evolution 39, 231e243.





































































































































































































































Russell, M.J., Hall, A.J., 1997. The emergence of life from iron monosulphide bubblesat a submarine hydrothermal redox and pH front. Journal of the GeologicalSociety 154, 377e402.

Russell, M.J., Hall, A.J., Cairnssmith, A.G., Braterman, P.S., 1988. Submarine hotsprings and the origin of life. Nature 336, 117-117.

Russell, M.J., Hall, A.J., Martin, W., 2010. Serpentinization as a source of energy at theorigin of life. Geobiology 8, 355e371.

Saito, T., 2007. Extremophile; the radioresistant mechanisms of the radioresistantbacteria. Viva Origino 35, 85e92.

Schlesinger, G., Miller, S.L., 1983. Prebiotic synthesis in atmospheres containing CH4,CO, and CO2. I. Amino acids. Journal of Molecular Evolution 19, 376e382.

Schoonen, M.A.A., Xu, Y., 2001. Nitrogen reduction under hydrothermal vent con-ditions: implications for the prebiotic synthesis of C-H-O-N compounds.Astrobiology 1, 133e142.

Sephton, M.A., 2002. Organic compounds in carbonaceous meteorites. NaturalProduct Reports 19, 292e311.

Sleep, N.H., Zahnle, K., 1998. Refugia from asteroid impacts on early Mars and theearly Earth. Journal of Geophysical Research 103, 28529e28544.

Smith, K.L., 1985. Deep-sea hydrothermal vent mussels: Nutritional state and dis-tribution at the galapagos rift. Ecology 66, 1067e1080.

Sutherland, J.D., 2016. The origin of lifedout of the Blue. Angewandte Chemie In-ternational Edition 55, 104e121.

Takahashi, E., 1986. Melting of a dry peridotite KLB-1 up to 14 GPa: implications onthe Origin of peridotitic upper mantle. Journal of Geophysical Research: SolidEarth 91, 9367e9382.

Takai, K., Gamo, T., Tsunogai, U., Nakayama, N., Hirayama, H., Nealson, K.H.,Horikoshi, K., 2004. Geochemical and microbiological evidence for a hydrogen-based, hyperthermophilic subsurface lithoautotrophic microbial ecosystem(HyperSLiME) beneath an active deep-sea hydrothermal field. Extremophiles 8,269e282.

Thomas-Keprta, K.L., Bazylinksli, D.A., Wentworth, S.J., Vali, H., Gibson, E.K.,Romanek, C.S., 2000. Elongated prismatic magnetite crystals in ALH84001carbonate globules: Potential Martian magnetofossils. Geochimica Et Cosmo-chimica Acta 64, 4049e4081.


Thomas-Keprta, K.L., Clemett, S.J., Bazylinski, D.A., Kirschvink, J.L., McKay, D.S.,Wentworth, S.J., Vali, H., Gibson, E.K., McKay, M.F., Romanek, C.S., 2001. Trun-cated hexa-octahedral magnetite crystals in ALH84001: Presumptive bio-signatures. Proceedings of the National Academy of Sciences 98, 2164e2169.

Thomas-Keprta, K.L., McKay, D.S., Wentworth, S.J., Stevens, T.O., Taunton, A.E.,Allen, C.C., Coleman, A., Gibson, E.K., Romanek, C.S., 1998. Bacterial minerali-zation patterns in basaltic aquifers: Implications for possible life in martianmeteorite ALH84001. Geology 26, 1031e1034.

Ueno, Y., Isozaki, Y., Yurimoto, H., Maruyama, S., 2001. Carbon isotopic signatures ofindividual archean microfossils(?) from Western Australia. International Geol-ogy Review 43, 196e212.

Wasson, J.T., Kyte, F.T., 1987. Comment on the letter “On the influx of small cometsinto the Earth’s atmosphere II: interpretation”. Geophysical Research Letters 14,779e780.

Weiss, B.P., Kirschvink, J.L., Baudenbacher, F.J., Vali, H., Peters, N.T., Macdonald, F.A.,Wikswo, J.P., 2000. A low temperature transfer of ALH84001 from Mars toEarth. Science 290, 791e795.

Wilde, S.A., Valley, J.W., Peck, W.H., Graham, C.M., 2001. Evidence from detritalzircons for the existence of continental crust and oceans on the Earth 4.4 Gyrago. Nature 409, 175e178.

Wirsen, C.O., Jannasch, H.W., Molyneaux, S.J., 1993. Chemosynthetic microbial ac-tivity at Mid-Atlantic Ridge hydrothermal vent sites. Journal of GeophysicalResearch 98, 9693e9703.

Woese, C.R., Fox, G.E., 1977. The concept of cellular evolution. Journal of MolecularEvolution 10, 1e6.

Woese, C.R., Kandler, O., Wheelis, M.L., 1990. Towards a natural system of organ-isms: proposal for the domains Archaea, Bacteria, and Eucarya. Proceedings ofthe National Academy of Sciences 87, 4576e4579.

Zahnle, K.J., Kasting, J.F., Pollack, J.B., 1988. Evolution of a steam atmosphere duringearth’s accretion. Icarus 74, 62e97.

Zel’dovich, Y.B., Khariton, Y.B., 1940a. On a chain decay of uranium under the actionof slow neutrons. Zhurnal Eksperimental’noi I Teoreticheskoi Fiziki 10, 29e36.

Zel’dovich, Y.B., Khariton, Y.B., 1940b. Fission and chain decay of uranium. UspekhiFizicheskikh Nauk 23, 329e357.































































































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Nine requirements for the origin of Earth's life: Not at the … · 2019-03-01 · Research Paper Nine requirements for the origin of Earth’s life: Not at the hydrothermal vent,